Function

A function is a well-defined process that always produces the same outputs when given the same inputs.

Functions may imply transformation when they either alter its participating entities or produce a new entity whose characteristics are influenced by the entities involved. An example of the latter is the production function.

A function can be contrasted with indistinct, undifferentiated processes that don't follow any particular order, don't or can't distinguish inputs, and therefore can't claim that its outputs are to any degree influenced by its inputs.

A function may or may not produce a different output from its input. A notable example of this is the identity function, which always produces an output equal to the input. While no transformation occurs, there must be a precise functioning in its definition and a specific set of possible inputs must be narrowed down so the identity function can be construed as effectively producing its intended output. This is the definining characteristic of a function, as opposed to processes in general.